This invention relates to a method and apparatus for the repair of tires, and more particularly to a method and apparatus for vulcanizing a repair patch on a tire.
In the repair of injured tires, whether bias-ply or radial, in which unvulcanized rubber patch material is used, various methods are employed to vulcanize the patch material to the injured area of the tire.
In some vulcanizing processes, a mold apparatus is utilized utilizing heat pads and air bags for applying heat to the rubber patch material.
In one process, a heated mandrel of solid material, such as metal, pre-shaped to fit the interior of the tire, is inserted within the tire. An external heat pad is placed against the exterior of the tire, and then an external air bag is placed against the external heat pad. The assembly is then placed within a solid mold and heat is applied to the solid mandrel in order to heat the patch material to a vulcanizing temperature.
In another form of the mold vulcanizing process, an internal heat pad may be placed against the patch material and the surrounding tire area and an inflatable mandrel or inflatable air bag placed within the tire. When the mandrel or air bag is inflated, pressure is applied against the internal heat pad. An external heat pad and an external air bag are retained against the exterior of the tire within the mold cavity of the mold apparatus, while the internal air bag or inflatable mandrel is clamped in place within the tire.
In one form of the mold vulcanization process, an inner tube has been substituted for the inflatable air bag mandrel for exerting pressure against the inside heat pad.
In all of the above mold vulcanization processes, both the external heat pad and the internal heat pad, although having some cross-sectional curvature, are made of solid rubber encasing the electrical heating coils and therefore have limited flexibility. Accordingly, when the heat pads are placed against the interior or the exterior surface of the tire, the heat pads are not flush with the corresponding surfaces of the tire. Since the tire curves in both its radial dimension and its circumferential dimension, the heat pads, although conforming to the shape to some degree in one dimension, do not conform to the shape in both dimensions of the tire. Accordingly, the heat pad bridges certain areas of the tire surfaces to create air gaps, and the heat is applied unevenly to the corresponding surfaces of the tire, creating localized hot spots.
Furthermore, because of the relative inflexibility of the conventional heat pads, they are not readily adaptable to fit tires of different sizes and shapes to compound the problem of even heat distribution to the repair area as well as the surrounding tire surfaces. Moreover, the relatively stiff heat pads cause distortions in the tire shape during the vulcanization process.
Because the patch on the interior surface of a tire projects inwardly beyond the plane of the tire surface, a rigid mandrel made of metal, or relatively inflexible heat pads, when applied to the interior surface of the injured area, creates uneven pressure against the raised patch and the surrounding tire surface, since the plane of the inner surface of the patch is not flush with the surrounding interior surface of the tire.
Examples of such mold apparatus are the Vulcan section repair molds manufactured and distributed by Vulcan Equipment Company, Limited, of Scarborough, Ontario, Canada.
Another disadvantage of the above mold-type repair apparatus is that the tire repairs have to be made at sites in which the tire mold apparatus is located, and field repairs would be highly impractical and expensive.
Another process of vulcanizing tire repairs, which can be accomplished in the field is the Monarch vulcanizing repair system produced by IMC (Engineers) Ltd., of Hartfordshire, England, and distributed in the United States. This system substitutes flexible, but inelastic, straps for the mold hardware for encircling the section of the tire to be repaired and for containing the exterior and interior heat pads, exterior and interior flat air bags and an inflatable mandrel fitted within the tire. The mandrel is inflated to exert pressure against the interior flat air bag and the interior heat pad, in a somewhat similar manner as the above-described processes incorporating the mold apparatus.